simulation method for simulating braking of a cable transport facility, a diagnosis method for diagnosing the braking of such a facility and control apparatus for controlling the facility

ABSTRACT

The application relates to a simulation method for simulating braking of a cable transport facility having at least one brake means and drive means, the simulation method comprising at least one test stage for testing the brake means, which test stage comprises at least one step of applying the brake means on the facility driven by the drive means controlled in a closed loop by a setpoint signal formed by a predetermined control curve F=f(t).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of International Application No. PCT/FR2007/001915, filed Nov. 21, 2007, which claims priority to French Patent Application No. 0610267, filed Nov. 23, 2006, both of which are incorporated herein by reference.

BACKGROUND AND SUMMARY

The invention relates to a simulation method for simulating braking of a cable transport facility. The invention also relates to a diagnosis method for diagnosing brake means, to an adjustment method for adjusting brake means by using said diagnosis method, and to control apparatus for controlling a cable transport facility that makes it possible to implement said simulation method.

For safety reasons, the brake means for braking a cable transport facility should be tested periodically. In order to perform such tests under conditions that are as close as possible to operating conditions, the braking should be tested while the facility is loaded. In the prior art, it is known that the transport facility can be ballasted before the testing operations are performed on the brake means. Such ballasting makes it possible to simulate normal operation of a facility driven while loaded. Unfortunately installing such ballast is a simulation operation that requires a large number of handling operations that increase the time and cost of testing the brake means.

An object of the invention is to remedy those problems by proposing a method of simulating braking of a transport facility that is simple, inexpensive, quick to implement, and accurate. To this end, in a first aspect, the invention provides a simulation method for simulating braking of a cable transport facility having at least one brake means and drive means, the simulation method comprising at least one step of applying the brake means on the facility driven by the drive means controlled in a closed loop by a setpoint signal formed by a predetermined control curve F=f(t). Thus, the drive means that continue to operate while the brake means are being applied can, in particular simulate the force of a load on the facility. This simulation makes it possible, in particular, to diagnose the brake means without having to ballast said facility.

In a first implementation, for the closed-loop control, the setpoint signal is compared with a measurement of the force exerted on the cable, of the drive torque, or of a variable that is characteristic of the drive means and that is proportional to the force exerted on the cable, to the drive torque, or to the instantaneous power delivered by the drive means. In a second implementation, for the closed-loop control, the setpoint signal is compared with a measurement of the speed of the cable. In a second aspect of the invention, the invention provides a diagnosis method for diagnosing at least one brake means of a cable transport facility having drive means, the diagnosis method comprising at least a test stage for testing the brake means, which test stage includes at least a simulation stage for simulation using the simulation method of the first aspect of the invention, performed on a facility driven while empty, and recording of a test characteristic curve.

Advantageously, the test stage further comprises a second step for comparing the test characteristic curve with a pre-recorded calibrated standard curve. Thus, the diagnosis of the brake means is performed simply, by comparing the test characteristic curve with an ideal curve or with a curve that is measured during a preliminary stage.

In a variant of the invention, the method further comprises a preliminary calibration stage comprising at least:

-   -   a step of recording the calibrated standard characteristic curve         while the brake means are being applied on the facility         operating while loaded; and     -   a step of recording the drive means control curve F=f(t) while         the brake means are being applied on the facility driven while         empty and by the drive means controlled in a closed loop by a         setpoint signal formed by said standard characteristic curve.         This preliminary stage makes it possible to take account of the         real characteristics of the facility, e.g. while it is being         commissioned, i.e. while it is being brought into service, and         avoids having to establish theoretical or ideal curves.

In another variant of the invention, the diagnosis method further comprises a preliminary calibration stage comprising at least:

-   -   a step of recording the drive means control curve F=f(t) while         the brake means are being applied on the facility while said         facility is operating loaded; and     -   a step of recording the calibrated standard characteristic curve         while the brake means are being applied on the facility driven         while empty and by the drive means controlled in a closed loop         by a setpoint signal formed by said control curve.

Advantageously, the preliminary stage further comprises a first step of adjusting the brake means. Thus, the method of the invention makes accurate diagnosis possible.

Advantageously, the preliminary stage further comprises a verification operation for verifying the calibration, which operation comprises:

-   -   a step of applying the brake means on the facility while the         facility is operating empty and while it is being driven by the         drive means controlled in a closed loop by a setpoint signal         formed by the control curve F=f(t) and of recording a         verification characteristic curve; and     -   a step of comparing the verification characteristic curve with         the calibration standard characteristic curve.         Thus, this operation makes it possible to validate the         consistency of the calibration stage. Advantageously, the         control curve F=f(t) is extended by a constant function K=f(t)         so as to extend the simulation for a longer time than the         deceleration time of the calibration step.

Advantageously, the test stage further comprises:

-   -   a step of applying the brake means on the facility while it is         operating empty, and of recording an empty characteristic curve;         and     -   a step of comparing the empty characteristic curve with a         pre-recorded empty calibrated standard characteristic curve.         The empty calibration standard characteristic curve is a curve         that is recorded while the brake means are being applied on the         facility operating empty. Thus, the method of the invention also         makes it possible to test the brake means on a facility that is         operating while empty.

In a first implementation, the characteristic curves are deceleration curves representing deceleration of the cable, and the control curve F=f(t) is recorded by measuring the force exerted on the cable, the drive torque, or a variable that is characteristic of the drive means and that is proportional to the force exerted on the cable, to the drive torque, or to the instantaneous power delivered by the drive means. In a second implementation, the characteristic curves are curves representing measurement of the force exerted on the cable, of the drive torque, or of a variable that is characteristic of the drive means, and that is proportional to the force exerted on the cable, to the drive torque, or to the instantaneous power delivered by the drive means, and the control curve F=f(t) is recorded by measuring the deceleration of the cable.

Advantageously, the method uses indexing of the position of at least one vehicle driven by the cable. Thus, the accuracy of the diagnosis is guaranteed because the various recordings can be made for similar load distributions on the cable. Advantageously, for a cable transport facility whose brake means are pneumatic or hydraulic means, the test stage further comprises a step of recording a pressure variations curve Pt=f(t) representing the pressure variations during application of the brake means, and a step of comparing Pt=f(t) with a predetermined curve Pe=f(t). The curve Pe=f(t) is a pressure variations curve recorded during the preliminary stage while the brake means are being applied. Thus, these curves make it possible to determine whether the operating differences observed are related to the hydraulic or pneumatic control means.

In a third aspect, the invention provides a method for adjusting at least one brake means of a cable transport facility, which method comprises:

-   -   at least a checking step for checking the brake means by using a         diagnosis method of the second aspect of the invention; and     -   at least an adjustment step for adjusting the brake means as a         function of the comparison of the deceleration curves Vec=f(t)         and Vtc=f(t).         Therefore, it is also possible to adjust the brake means         accurately.

Finally in a fourth aspect, the invention provides control apparatus for controlling a cable transport facility having drive means and at least one brake means, the apparatus comprising control means for controlling the drive means, control means for controlling the brake means, and a safety device. The control apparatus further comprises switch means for switching the safety device between an active position in which simultaneous use of the drive means and of the brake means is not allowed, and a passive position in which said simultaneous use is allowed. Advantageously, the apparatus further comprises measurement means for measuring the speed of the cable, data recording means, pressure measurement means, current measurement means for measuring the current passing through the drive means, and position-indexing means for indexing the position of at least one vehicle.

BRIEF DESCRIPTION OF DRAWINGS

Other objects and advantages of the invention appear from the following description given with reference to the accompanying drawings, in which:

FIG. 1 shows a characteristic curve in a first implementation of the invention, which curve was recorded during application of the brake means on the facility operating while loaded, said characteristic curve being a cable deceleration curve Vec=f(t);

FIG. 2 shows the calibrated standard deceleration curve Vec=f(t) of FIG. 1 and a drive means control curve F=f(t) recorded during application of the brake means on a facility driven while not loaded and by drive means controlled in a closed loop by a setpoint signal formed by the deceleration curve Vec=f(t);

FIG. 3 shows the calibrated standard deceleration curve Vec=f(t), the drive means control curve F=f(t) and a cable deceleration curve Vv=f(t) recorded during a calibration verification operation; and

FIG. 4 shows the curves of FIGS. 1 and 2 and three deceleration test curves Vtc=f(t) when braking is too hard, adjusted correctly, or too soft.

DETAILED DESCRIPTION

The term “closed loop” is used in the following detailed description to mean a servo-control loop that compares a setpoint magnitude with an output magnitude in order to cause the output value to tend towards the setpoint value. In addition, in the following description, when mention is made of a variable that is characteristic of the drive means and that is proportional to the force exerted on the cable, or to the drive torque, such a variable might, depending on the type of power supply chosen for the drive means, be an electrical control variable such as the modulation frequency of a converter powering the drive means, or a variable voltage or current for powering the drive means. It might also be a mechanical variable that is measured directly on the facility, such as the tension force of the drive cable or the torque of the drive means.

A cable transport facility is generally made up of at least two stations between which at least one moving haulage cable forms a loop in order to haul one or more vehicles, e.g. one or more cable cars, from one station to another. Optionally, the vehicles can be suspended from the moving cable that drives them. Alternatively, as is common practice for large-capacity facilities, the vehicles can be suspended from stationary cables via suspension arms equipped with wheels, and can be driven along the stationary cables by the moving haulage cable.

Drive means make it possible to drive the cable. For example, the drive means are made up of one or more electric motors, of a drive pulley, and of a declutchable transmission device for transmitting the movement between the motor(s) and the drive pulley. In addition, the facility is equipped with brake means. The brake means can normally comprise one electromagnetic brake consisting in interrupting the power supply to the motors, one or more service brakes that are applied for normal stops of the facility, and one or more emergency brakes.

In an implementation of the invention, the service brake acts on the transmission shaft of the drive means whereas the emergency brake acts directly on the drive pulley. In a variant implementation, the brake means are hydraulic or pneumatic brakes. For example, the brake means are brake means that are caused to open by hydraulic or pneumatic means such as actuators, mechanical return means such as springs making it possible to urge the brake means back towards their braking closed position.

The facility also has control apparatus for controlling the transport facility. The apparatus comprises at least control means for controlling the drive means and control means for controlling the brake means. Advantageously, the control apparatus further comprises a safety device that, when in an active position, makes it possible to interrupt the power supply to the drive means as soon as brake means are actuated. The method of the invention includes steps during which the drive means have to operate simultaneously with the brake means. Therefore, the control apparatus of the facility includes a switch device for switching the safety device between its active position and a passive position in which simultaneous operation of the drive means and of brake means is allowed. The control apparatus also includes diagnosis apparatus. The diagnosis apparatus includes data recording means, is connected to the drive means and to the brake means, and receives information from measurement means for measuring the speed of the cable, from measurement means for measuring a variable that is characteristic of the drive means, from indexing means for indexing the positions of the vehicles, and from measurement means for measuring the pressure in the brake means.

In an implementation, the variable that is characteristic of the drive means is the current passing through the drive means. In a variant, the control and diagnosis apparatus is made up of a console and of a control automatic logic controller. However, it should be noted that the invention is not limited to this embodiment, and any suitable computer-science or electronic control apparatus can be used. In an advantageous implementation of the invention, the diagnosis method for diagnosing brake means includes a preliminary calibration stage that can be performed on bringing the facility into service, i.e. on commissioning it.

During the calibration stage, the brake means of the facility are pre-adjusted to the regulatory settings. The calibration stage then includes a first step during which brake means are applied on the facility operating while loaded and a calibrated standard characteristic curve is recorded. In the embodiment shown, the calibrated standard characteristic curve is a cable deceleration curve Vec=f(t) (referenced 1 in FIG. 1). During this step, it should be noted that the drive means are stopped while the brake means are being applied. If the brake means are pneumatic or hydraulic means, it is also possible, in this step, to record a pressure variation curve Pe=f(t) plotting the pressure variation in the brake means while they are being applied on the facility.

During a second step, the brake means are applied on the facility driven while empty and by drive means controlled in a closed loop by a setpoint signal formed by the calibrated standard characteristic curve: the deceleration curve Vec=f(t) in the implementation shown. The closed-loop control apparatus compares the real deceleration of the cable with the setpoint deceleration Vec=f(t) and causes the drive means to operate in such a manner as to obtain a real deceleration corresponding to the setpoint. During this step, the drive means control curve F=f(t) (referenced 2 in FIG. 2) is recorded.

In the first implementation shown in FIG. 2, the control curve 2 corresponds to the variation in the magnitude of the electrical current passing through the drive means. However, it should also be noted that said control curve can also be obtained by measuring any variable related to the force exerted by the drive means on the cable, or to the drive torque, or to the instantaneous power delivered by the drive means. It should be noted that the calibration stage thus makes it possible to obtain a control curve F=f(t) (referenced 2) for control of the drive means that makes it possible to simulated the force of a load while the brake means are applied on a facility operating while empty. In addition, it should be noted that the control curve F=f(t) is extended by a constant function K=f(t) referenced 7, making it possible to simulate the load for a longer time than the time for which the cable decelerates during the second calibration step. In addition, during said second step, it is also possible to record the pressure variation curve Pe1=f(t) and to verify that it corresponds to the previously recorded curve Pe=f(t).

Preferably, provision is also made to verify the calibration by recording a verification characteristic curve while the brake means are being applied on the facility driven empty and by drive means controlled in a closed loop by a setpoint signal formed by the control curve F=f(t) referenced 2, as setpoint signal. For the implementation shown, the verification characteristic curve corresponds to the cable deceleration curve Vv=f(t) referenced 6. During this verification, a verification characteristic curve (FIG. 3) and optionally a pressure curve Pe2=f(t) are measured. If the verification characteristic curve coincides with the calibrated standard characteristic curve, it is then possible to validate the calibration. In an implementation of the invention, it is also verified that the pressure curves Pe=f(t) and Pe2=f(t) match.

The diagnosis method includes at least one test step for testing the brake means. This test step can, in particular, be performed periodically in order to verify that the adjustment of the brake complies with the regulatory adjustment settings. During the test step, on a facility driven while empty, a simulation operation is performed to simulate braking performed on a facility driven while loaded. For this purpose, the brake means are applied on a facility driven while empty and by drive means controlled in a closed loop by a setpoint signal formed by the previously recorded control curve F=f(t). Thus, during this step, the drive means simulate the force of the load and a test characteristic curve is recorded.

In the implementation shown in FIG. 4, three test characteristic curves formed by cable deceleration curves Vtc=f(t) referenced 3, 4, and 5 are shown. In order to determine whether the adjustment of the brakes complies, the test characteristic curve Vtc=f(t) referenced 3, 4, or 5 is compared with the calibrated standard characteristic curve Vec=f(t).

In FIG. 4, the first curve 3 has a gradient that is steeper than the gradient of the calibrated standard curve Vec=f(t) and shows a situation in which braking is too hard. The second curve 4 has a gradient of the same order as the gradient of the calibrated standard curve Vec=f(t) and shows a situation in which the braking is adjusted correctly. Finally, the third curve 5 has a gradient that is shallower than the gradient of the calibrated standard curve Vec=f(t) and shows a situation in which the braking is too soft. As a function of the comparison of the curves Vec=f(t) and Vtc=f(t), it is then possible to adjust the brake means to the correct setting.

Advantageously, the test stage also includes a recording step for recording a pressure curve Pt=f(t) in the brake means. The curve Pt=f(t) is then compared with the calibrated standard pressure curve Pe=f(t). It is thus possible to deepen the diagnosis of the brake means by determining whether the deviations observed between the curves Vec=f(t) and Vtc=f(t) are related to the hydraulic or pneumatic control means.

In an implementation of the invention, the diagnosis method can also include the preliminary test of the brake means on the facility operating empty. To this end, a calibrated standard characteristic curve is recorded while the brake means are being applied on the facility operating empty during the preliminary calibration stage. In the implementation shown, the empty standard characteristic curve is a deceleration curve Vev=f(t). Then, during the test stage, a characteristic curve is recorded while the brake means are being applied on a facility operating empty, in this example a deceleration curve Vtv=f(t). The characteristic curves Vev=f(t) and Vtv=f(t) are then compared in order to detect any incorrect adjustment of the brake means.

In a second implementation (not shown), the characteristic curves can be measurement curves representing measurements of the force exerted on the cable, of the drive torque, or of a variable that is characteristic of the drive means and proportional to the force exerted on the cable or to the drive torque. In this situation, the control curve corresponds to a deceleration curve representing deceleration of the cable. However, it should be noted that, for this implementation, interpretation of the comparison between the calibrated standard curve and the test characteristic curve is less easy. It should also be noted that, in this case, during the calibration stage, the drive means control curve F=f(t) is recorded while the brake means are being applied on the facility operating while loaded. Then, during the second step, a standard characteristic curve is recorded while the brake means are being applied on the facility driven while empty and by the drive means controlled in a closed loop by a setpoint signal formed by the previously recorded control curve.

Advantageously, the diagnosis method of the invention makes it possible to test the adjustment of the various brake means of the facility, such as the electromagnetic brake, the emergency brake(s), and the service brake(s). For this purpose, the method makes provision to record, for each type of brake means, the deceleration curves Vec=f(t), Vtc=f(t), Vv=f(t), Vev=f(t), Vtv=f(t) referenced 1, 3, 4, 5, and 6, and the drive means control curve F=f(t) referenced 2. Thus, the adjustment of each brake means can be tested independently.

In order to establish accurate diagnosis of the brake means, it is advantageous for the position(s) of the vehicle(s) on the cable to be indexed accurately such that all of the applications of the brake means performed for the needs of the method are effected for similar load distributions on the cable. Furthermore, it should be noted that when the brake means to be tested do not operate in all-or-nothing mode, the brake means should be applied to identical levels in the context of the diagnosis method. It should also be noted that, when the brake means are means controlled by modulating the force as a function of the deceleration of the line, it is necessary to suspend the modulation before performing the method of diagnosing the brake means. However, the simulation method of the invention also makes it possible to diagnose the modulation of the force as a function of the deceleration of the line. When the drive means are controlled in a closed loop by a setpoint signal formed by a control curve F=f(t) which is a deceleration curve, it is possible to test the modulation apparatus by causing the control curve F=f(t) to vary relative to a control curve Fe=f(t) recorded during the calibration stage and by observing the response of the modulation apparatus.

The mathematical demonstration making it possible to validate the above-described diagnosis method is as follows:

During the preliminary stage, when the brake means are applied on the facility operating empty and Vec=f(t) is recorded, it is possible to write the following relationship:

Fc+Ffe=Mc*αec  (a)

Where:

Fc: force generated by the load on the facility operating while loaded;

Ffe: calibrated standard braking force

M: mass of the cable and of the vehicles; and

α: acceleration of the cable.

Similarly, when the brake means are applied on a facility operating empty, it is possible to write the following relationship:

Fv+Ffe=Mv*αv  (b)

Where:

Fv: force generated by the load of the empty facility.

During the preliminary calibration stage, when the drive means are controlled with, as a setpoint signal, the deceleration curve Vec=f(t) referenced 1, it is possible to write the following relationship:

Fmot+Fv+Ffe=Mv*αec  (c)

or Fmot=Mv*αec−Fv−Ffe  (c′)

where Fmot: force generated by the motor.

Finally, during the test stage, when the drive means are controlled with the control curve F=f(t) referenced 2 and when the curve Vtc=f(t) referenced 3, 4, 5 is measured, it is possible to write the following relationship:

Fmot+Fv−Fft=Mv*αtc  (d)

By replacing Fmot of the relationship c′:

Mv*αec−Fv−Ffe−Fv−Fft=Mv*αtc

Mv*αec−Ffe−Fft=Mv*αtc

Thus, if the curves Vec=f(t) and Vtc=f(t) are similar, then αec=atc. Therefore, the braking force of the tested brake means is equal to the calibrated standard braking force of the brake means: Fft=Ffe. In which case, the brake means are thus adjusted correctly. 

1. A simulation method for simulating braking of a cable transport facility having at least one brake and a drive, the simulation method comprising at least one step of applying the brake on the facility driven by the drive controlled in a closed loop by a setpoint signal formed by a predetermined control curve F=f(t).
 2. A simulation method according to claim 1, wherein, for the closed-loop control, the setpoint signal is compared with a measurement of the force exerted on the cable, of the drive torque, or of a variable that is characteristic of the drive and that is proportional to the force exerted on the cable, to the drive torque, or to the instantaneous power delivered by the drive.
 3. A simulation method according to claim 1, wherein, for the closed-loop control, the setpoint signal is compared with a measurement of the speed of the cable.
 4. A diagnosis method for diagnosing at least one brake of a cable transport facility having at least one brake and a drive, the diagnosis method comprising at least a test stage for testing the brake, which test stage includes at least applying the brake on the facility driven by the drive controlled in a closed loop by a setpoint signal formed by a predetermined control curve F=f(t), while the facility is empty, and recording of a test characteristic curve.
 5. A diagnosis method according to claim 4, wherein the test stage further comprises a second step for comparing the test characteristic curve with a pre-recorded calibrated standard curve.
 6. A diagnosis method according to claim 4, further comprising a preliminary calibration stage comprising at least: a step of recording the calibrated standard characteristic curve while the brake is being applied on the facility operating while loaded; and a step of recording the drive control curve F=f(t) while the brake is being applied on the facility driven while empty and by the drive controlled in a closed loop by a setpoint signal formed by said standard characteristic curve.
 7. A diagnosis method according to claim 4, further comprising a preliminary calibration stage comprising at least: a step of recording the drive control curve F=f(t) while the brake is being applied on the facility while said facility is operating loaded; and a step of recording the calibrated standard characteristic curve while the brake is being applied on the facility driven while empty and by the drive controlled in a closed loop by a setpoint signal formed by said control curve.
 8. A diagnosis method according to claim 6, wherein the preliminary stage further comprises a first step of adjusting the brake.
 9. A diagnosis method according to claim 7, wherein the preliminary stage further comprises a verification operation for verifying the calibration, which operation comprises: a step of applying the brake on the facility while the facility is operating empty and driven by the drive controlled in a closed loop by a setpoint signal formed by the control curve F=f(t) and of recording a verification characteristic curve; and a step of comparing the verification characteristic curve with the calibration standard characteristic curve.
 10. A diagnosis method according to claim 4, wherein the test stage further comprises: a step of applying the brake on the facility while empty, and of recording an empty characteristic curve; and a step of comparing the empty characteristic curve with a pre-recorded empty calibrated standard characteristic curve.
 11. A diagnosis method according to claim 10, wherein the empty calibration standard characteristic curve is a curve that is recorded while the brake is being applied on the facility operating empty.
 12. A diagnosis method according to claim 4, wherein the characteristic curves are deceleration curves representing deceleration of the cable.
 13. A diagnosis method according to claim 12, wherein the control curve F=f(t) is recorded by measuring the force exerted on the cable, the drive torque, or a variable that is characteristic of the drive and that is proportional to the force exerted on the cable, to the drive torque, or to the instantaneous power delivered by the drive.
 14. A diagnosis method according to claim 4, wherein the characteristic curves are curves representing measurement of the force exerted on the cable, of the drive torque, or of a variable that is characteristic of the drive, and that is proportional to the force exerted on the cable, to the drive torque, or to the instantaneous power delivered by the drive.
 15. A diagnosis method according to claim 14, wherein the control curve F=f(t) is recorded by measuring the deceleration of the cable.
 16. A diagnosis method according to claim 4, wherein the control curve F=f(t) is extended by a constant function K=f(t).
 17. A diagnosis method according to claim 4, wherein the position of at least one vehicle driven by the cable is indexed.
 18. A diagnosis method according to claim 4, for a cable transport facility whose brake is pneumatic or hydraulic, wherein the test stage further comprises a step of recording a pressure variations curve Pt=f(t) representing the pressure variations during application of the brake, and a step of comparing Pt=f(t) with a predetermined curve Pe=f(t).
 19. A diagnosis method according to claim 18, wherein the curve Pe=f(t) is a pressure variations curve recorded during the preliminary stage while the brake is being applied.
 20. An adjustment method for adjusting at least one brake of a cable transport facility, which method comprises: at least a checking step for checking the brake by using a diagnosis method according to claim 4; and at least an adjustment step for adjusting the brake as a function of the comparison of the test characteristic and standard characteristic curves.
 21. A control apparatus for controlling a cable transport facility having a drive and at least one brake, the apparatus comprising a control operably controlling the drive, a control operably controlling the brake, and a safety device, the control apparatus further comprising a switch operably switching the safety device between an active position in which simultaneous use of the drive and of the brake is not allowed, and a passive position in which said simultaneous use is allowed.
 22. A control apparatus according to claim 21, further comprising a measurer operably measuring the speed of the cable.
 23. A control apparatus according to claim claim 21, further comprising a data recorder.
 24. A control apparatus according to claim 21, further comprising a pressure measurer.
 25. A control apparatus according to claim 21, further comprising a current measurer operably measuring the current passing through the drive.
 26. A control apparatus according to claim 21, further comprising a position-indexer operably indexing the position of at least one vehicle driven by the cable. 